Shake all ingredients with ice and strain into a frozen coupe glass.
Garnish with a tiny sprinkle of ground cinnamon.
1. The Gin. I bought a jar of Moroccan-style olives, poured out all of the brine, refilled the jar with gin, and let it "steep" for at least a week.
2. The Grapefruit. This particular grapefruit has a tiny bit of sweetness.
3. The sherry vinegar. I found this particular "high performance" version a few years ago and it really makes a difference. You don't want "vinegar." Rather, you want a very flavorful Sherry vinegar.